Denitrification and nitrous oxide cycling within the upper oxycline of the eastern tropical South Pacific oxygen minimum zone

Farı́as, Laura; Castro-González, Maribeb; Cornejo, Marcela; Charpentier, J.; Faúndez, Juan; Boontanon, Narin; Yoshida, Naohiro

doi:10.4319/lo.2009.54.1.0132

Cited by 102 publications

(115 citation statements)

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“…Anaerobic reactions are generally thought to be inhibited in waters with more than 3−5 mmol·m −3 O 2 (7,18). However, thresholds up to around 20 mmol·m −3 for anammox and DNRN (19) and around 40 mmol·m −3 for denitrification (20) have been reported, perhaps as a result of anoxic microenvironments within sinking aggregates. In the rest of the paper, we focus on waters with oxygen concentrations between 0 mmol·m −3 and 10 mmol·m −3 , which are common in upper-ocean OMZs, and where DVM are observed.…”

Section: Dvm Association With Anoxic Watersmentioning

confidence: 99%

Enhancement of anammox by the excretion of diel vertical migrators

Bianchi

Babbin

Galbraith

2014

Proc. Natl. Acad. Sci. U.S.A.

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Measurements show that anaerobic ammonium oxidation with nitrite (anammox) is a major pathway of fixed nitrogen removal in the anoxic zones of the open ocean. Anammox requires a source of ammonium, which under anoxic conditions could be supplied by the breakdown of sinking organic matter via heterotrophic denitrification. However, at many locations where anammox is measured, denitrification rates are small or undetectable. Alternative sources of ammonium have been proposed to explain this paradox, for example through dissimilatory reduction of nitrate to ammonium and transport from anoxic sediments. However, the relevance of these sources in open-ocean anoxic zones is debated. Here, we bring to attention an additional source of ammonium, namely, the daytime excretion by zooplankton and micronekton migrating from the surface to anoxic waters. We use a synthesis of acoustic data to show that, where anoxic waters occur within the water column, most migrators spend the daytime within them. Although migrators export only a small fraction of primary production from the surface, they focus excretion within a confined depth range of anoxic water where particle input is small. Using a simple biogeochemical model, we suggest that, at those depths, the source of ammonium from organisms undergoing diel vertical migrations could exceed the release from particle remineralization, enhancing in situ anammox rates. The contribution of this previously overlooked process, and the numerous uncertainties surrounding it, call for further efforts to evaluate the role of animals in oxygen minimum zone biogeochemistry.anammox | denitrification | oxygen minimum zone | diel vertical migration W ater column oxygen minimum zones (OMZs), where oxygen concentrations plummet to submicromolar levels (1), are responsible for approximately one-third of the total removal of fixed nitrogen from the oceans (2, 3). Several processes mediated by specialized prokaryotes convert fixed inorganic nitrogen (NH 4 + , NO 2 − , and NO 3 − ) to N 2 in anoxic waters. Canonical denitrification, consisting of dissimilatory NO 3 − reduction to NO 2 − (DNRN) followed by the further oxidation of organic matter with NO 2 − (the denitrification step), was long considered the dominant fixed N removal pathway in anoxic waters. Over the last decade, anammox has gained attention as a major sink of fixed N in nearly anoxic waters (O 2 < 10 mmol·m −3 ) (4, 5).Stoichiometric considerations would suggest a close coupling between denitrification and anammox (6, 7). Under anoxic conditions, the NH 4 + liberated by the remineralization of organic matter through DNRN and denitrification should accumulate in the water column because conventional (aerobic) nitrification cannot proceed. However, this accumulation is not observed in the cores of anoxic waters, where observed NH 4 + concentrations are generally much less than 1 mmol·m −3 (8). In these regions, oxidation of NH 4 + with NO 2 − by anammox is thought to be the major sink of NH 4 + (9). Given that no significant NH 4 + acc...

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Section: Dvm Association With Anoxic Watersmentioning

confidence: 99%

Enhancement of anammox by the excretion of diel vertical migrators

Bianchi

Babbin

Galbraith

2014

Proc. Natl. Acad. Sci. U.S.A.

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“…This kind of O 2 distribution triggers intense nitrogen species cycling, particularly for N 2 O. In these zones, N 2 O levels can drop up to 20 times in less than 50 m depth (Farías et al, 2009). Thus, it is common to observe a zone of high N 2 O production and accumulation located at the oxyclines, but below those there is intense N 2 O consumption and depletion at the OMZ's core.…”

Section: Introductionmentioning

confidence: 99%

“…Many of these areas are associated with eastern boundary upwelling ecosystems, which are major sources of oceanic atmospheric N 2 O (Naqvi et al, 2010). This is the case of the OMZ in the eastern South Pacific (ESP) where intense N 2 O exchange with the atmosphere has been reported (Farías et al, 2009). The ESP's OMZ is characterized by O 2 concentrations as low as 2 nM at its core (Revsbech et al, 2009), being one of the most intense and shallow in the world ocean (upper boundary as shallow as 50 m; Morales et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

“…Thus, it is common to observe a zone of high N 2 O production and accumulation located at the oxyclines, but below those there is intense N 2 O consumption and depletion at the OMZ's core. Within the core, O 2 concentration has been reported to be lower than 0.5 µM (Codispoti and Christensen, 1985;Naqvi and Noronha, 1991;Farías et al, 2009), and even as low as nanomolar concentrations (Thamdrup et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

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Following the N2O consumption in the oxygen minimum zone of the eastern South Pacific

Cornejo¹

2012

Biogeosciences

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“…Four main pathways have been described as leading to N 2 O production ; and 4) nitrifier denitrification. But so far, only one process -total denitrification -is known to consume N 2 O by reducing it to N 2 under extremely low O 2 (<4.4 µM) or suboxic conditions (Elkins et al, 1978;Farías et al, 2009). Thus, the amount of N 2 O in the ocean depends on a balance of N 2 O production and consumption processes.…”

Section: N 2 O and Ch 4 Cycling In The Water Columnmentioning

confidence: 99%

Chemolithoautotrophic production mediating the cycling of the greenhouse gases N2O and CH4 in an upwelling ecosystem

Farı́as¹,

Fernández

Faúndez³

et al. 2009

Biogeosciences

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Abstract. The high availability of electron donors occurring in coastal upwelling ecosystems with marked oxyclines favours chemoautotrophy, in turn leading to high N 2 O and CH 4 cycling associated with aerobic NH + 4 (AAO) and CH 4 oxidation (AMO). This is the case of the highly productive coastal upwelling area off central Chile (36 • S), where we evaluated the importance of total chemolithoautotrophic vs. photoautotrophic production, the specific contributions of AAO and AMO to chemosynthesis and their role in gas cycling. Chemolithoautotrophy was studied at a time-series station during monthly (2007)(2008)(2009)) and seasonal cruises (January 2008, September 2008, January 2009) and was assessed in terms of the natural C isotopic ratio of particulate organic carbon (δ 13 POC), total and specific (associated with AAO and AMO) dark carbon assimilation (CA), and N 2 O and CH 4 cycling experiments. At the oxycline, δ 13 POC averaged −22.2‰; this was significantly lighter compared to the surface (−19.7‰) and bottom layers (−20.7‰). Total integrated dark CA in the whole water column fluctuated between 19.4 and 2.924 mg C m −2 d −1 , was higher during active upwelling, and contributed 0.7 to 49.7% of the total integrated autotrophic CA (photo plus chemoautotrophy), which ranged from 135 to 7.626 mg C m −2 d −1 , and averaged 20.3% for the whole sampling period. Dark CA was reduced by 27 to 48% after adding a specific AAO inhibitor (ATU) and by 24 to 76% with GC7, a specific archaea inhibitor. This indicates that AAO and AMO microbes (most of them archaea) were performing dark CA through the oxidation of NH

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Denitrification and nitrous oxide cycling within the upper oxycline of the eastern tropical South Pacific oxygen minimum zone

Cited by 102 publications

References 50 publications

Enhancement of anammox by the excretion of diel vertical migrators

Enhancement of anammox by the excretion of diel vertical migrators

Following the N<sub>2</sub>O consumption in the oxygen minimum zone of the eastern South Pacific

Chemolithoautotrophic production mediating the cycling of the greenhouse gases N<sub>2</sub>O and CH<sub>4</sub> in an upwelling ecosystem

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Denitrification and nitrous oxide cycling within the upper oxycline of the eastern tropical South Pacific oxygen minimum zone

Cited by 102 publications

References 50 publications

Enhancement of anammox by the excretion of diel vertical migrators

Enhancement of anammox by the excretion of diel vertical migrators

Following the N&lt;sub&gt;2&lt;/sub&gt;O consumption in the oxygen minimum zone of the eastern South Pacific

Chemolithoautotrophic production mediating the cycling of the greenhouse gases N&lt;sub&gt;2&lt;/sub&gt;O and CH&lt;sub&gt;4&lt;/sub&gt; in an upwelling ecosystem

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Following the N<sub>2</sub>O consumption in the oxygen minimum zone of the eastern South Pacific

Chemolithoautotrophic production mediating the cycling of the greenhouse gases N<sub>2</sub>O and CH<sub>4</sub> in an upwelling ecosystem